1. Field of the Invention
The present invention relates to a shift-by-wire system that is mounted in a vehicle and that actuates an object of actuation by driving a manual shaft on the basis of a shifting manipulation.
2. Description of the Related Art
In the past, as this type of shift-by-wire system, a shift-by-wire system that includes a spool position sensor which detects the position of a spool to be used to switch shift positions, and that when any of a parking (P) position, a reverse (R) position, an neutral (N) position, and a drive (D) position is selected using a selector switch (shift switch), controls a motor so that the spool will be located at a position associated with the selected position on the basis of a signal sent from the spool position sensor has been proposed (refer to, for example, JP-A-2007-139102 (patent document 1)). In this system, position switching edges are associated with the D position and P position respectively, and a regulation unit (stopper) is included to regulate the rotation of the motor at the position switching edges. When an abnormality occurs in the position sensor, if the selector switch is set to the D position, the motor is driven until a movement is regulated to a D-position direction. If the selector switch is not set to the D position, the motor is driven until a movement is regulated to a P-position direction (a reverse rotating direction with respect to the D-position direction). Thus, the abnormality in the spool position sensor is coped with.
As for the foregoing shift-by-wire system, a description has been made of a countermeasure to be taken when an abnormality occurs in the spool position sensor but has not been made of a case where an abnormality occurs in a motor angle sensor to be used to control a brushless motor which drives the spool. When an abnormality occurs in the motor angle sensor, driving the motor is thought to be ceased. However, when consideration is taken into the fact that the shift-by-wire system is mounted in a vehicle, it is desired that even if an abnormality occurs in the motor angle sensor, evacuative driving is enabled or any other appropriate measure is taken.